Access gateways are widely used to connect devices in a home of a customer to the Internet or any other wide area network (WAN). Access gateways use for example digital subscriber line (DSL) technology that enables a high data rate transmission over copper lines. During the years, several DSL standards have been established differing in data rates and in range, for example ADSL (Asymmetric digital subscriber line), ADSL2, VDSL (Very High Speed Digital Subscriber Line) and VDSL2, which are referred to in this context as xDSL. Network operators, e.g. Internet service providers, are managing a large amount, up to millions, of residential gateways, also other devices such as routers, switches, telephones and set-top boxes, which are understood in this context as customer premises equipment (CPE) devices.
Fiber to the distribution point (FTTdp) is bringing the fiber optic connection of the service providers closer to the home of the customer. However, the last few 100 meters of the broadband connection are still handled by the existing copper wire to the home: currently being used for legacy technologies such as Public Switched Telephone Network (PSTN) and xDSL.
In order to match the increased speed capabilities that come with bringing the fiber nodes closer to the home, the technology on the copper wire is also evolving to higher speeds. This is the base for the introduction of G.fast as an improved access technology on the copper wire. Formal specifications for G.fast have been drafted as ITU-T G.9700 and G.9701.
FIG. 1 shows the migration from copper links to fiber links closer to the home. For G.fast, a Distribution Point Unit (DPU) provides the link between the optical fiber of the Central Office (CO) with the CPE of the customer. In order to enable a flexible deployment of the DPU close to the home of the customer, the G.fast standardization foresees reverse power feeding for the DPU. In this scenario, the DPU is powered by the CPE, or a separate power injector located at the customer's premises. This enables a flexible placement of the DPU and allows for multiple subscribers to provide power for a DPU.
The benefits of using reverse power feeding lie mainly in flexibility and cost advantages, but several challenges arise. There are safety requirements that need to be met, for example since power is running on the telephone wires, a user might be exposed, or old legacy equipment that might still be connected to the telephone wire might be damaged by this power. Other important aspects to be considered are that the CPE devices can be located at different ranges from the DPU and each cable might have different physical characteristics: diameter, impedance, power loss.
There exists also a conflict between the current telephone system PSTN and the reverse power feeding of the DPU, as illustrated in FIG. 2. An access gateway 2 operates with a digital subscriber line access multiplexer (DSLAM) providing a PSTN service and a VDSL service via a copper line to the access gateway 2, or operates alternatively with a DPU 1 providing a G.fast service. Because the PSTN service includes a 48 V DC-voltage, the PSTN service cannot operate in parallel with the G.fast service provided by the DPU 1 because of the reverse power feeding of the access gateway 2. Service providers and customers need to be aware of this deployment scenario and have to adapt accordingly.
U.S. Pat. No. 8,601,289 discloses an optical network comprising a DPU and a plurality of CPE devices, each CPE device having a reverse power supply and each being connected to a copper wire pair and configured to transmit and receive data and provide reverse power over the wire pair. A power management circuit of the DPU is provided being configured to receive power and to provide power sharing and manage power consumption and power supply redundancy from the plurality of CPE devices.